CH-A-650,280 describes a drawing frame which, for each pair of rollers, has a separate drive motor, the speed of which is adjustable by means of a frequency divider. A computer containing an input and an indicator device calculates the speed ratios for the motors according to the input data and adjusts the drawing frame accordingly. The computer can also be assigned a measuring member for the fineness of the fibre sliver, from the measurement signal of which can be derived a non-uniformity signal characterising the non-uniformity of the fibre sliver.
When deviations of the draw from the input values occur on this drawing frame, these can be recognised only indirectly from their effects on the non-uniformity of the fibre sliver. This method of regulating the draw by means of the fibre sliver constitutes a so-called long-time regulation which, in view of its inertia, cannot satisfy the practical demands for a regulation of the draw. In addition, the deviations in the draw become noticeable as non-uniformity of the sliver only when a particular value is exceeded, and therefore, in particular, a drift of the system as a whole can be recognised only with great difficulty by means of the non-uniformity of the sliver.